1. Field of Invention
The present invention relates to a current driving system of a light emitting diode (LED) applied to a measurement apparatus for measuring the concentration of light absorbing material in a living tissue, the measurement apparatus having a main body for calculating the concentration of light absorbing material in a living tissue.
2. Related art
As a common example of the measurement apparatus for measuring the concentration of light absorbing material in a living tissue, there is conventionally provided a pulse oximeter by which the oxygen saturation in arterial blood is measured. This pulse oximeter is known as a measurement apparatus by which the oxygen saturation in arterial blood (SpO2) can be continuously measured non-invasively into an artery by utilizing a variation of blood volume in the artery caused by pulsation.
In this case, the oxygen saturation (SpO2) represents a ratio (%) of hemoglobin contained in blood which is combined with oxygen. Hemoglobin combined with oxygen is referred to as oxyhemoglobin (HbO2), and hemoglobin not combined with oxygen is referred to as deoxyhemoglobin (Hb).
However, red of blood is the color of hemoglobin. Therefore, oxyhemoglobin absorbs less red light, and deoxyhemoglobin absorbs much red light. Accordingly, arterial blood containing much oxygen absorbs less red light because a ratio of oxyhemoglobin is high. Therefore, arterial blood containing much oxygen appears brightly red. On the other hand, venous blood in which oxygen has already been consumed appears dark because it contains much deoxyhemoglobin. As described above, the color of blood reflects the degree of combination of hemoglobin with oxygen, that is, the color of blood reflects the oxygen saturation.
When the pulse oximeter is used, it is possible to obtain only information of arterial blood by using light electric pulses. According to the pulse oximeter, measurement is made in such a manner that a relatively thin portion of a human body such as a finger is irradiated with light and an intensity of transmitted light is measured, that is, light electric pulses are recorded. In this case, the light absorbing characteristic of blood is changed by the oxygen saturation. Even in the case of the pulsation of the same variation of blood volume, the obtained pulse wave amplitude is different according to the oxygen saturation of the blood.
As shown in FIG. 16, in general, the pulse oximeter includes: a probe 10 attached to a patient; and a measurement apparatus body 20. The probe 10 is composed of a light emitting section 12 and a light receiving section 14. A portion of a human body to be measured such as a finger, that is, a living tissue is interposed between the light emitting section 12 and the light receiving section 14. In the light emitting section 12, there are provided two light emitting diodes (LED 1 and LED 2). One is a light emitting diode LED 1, the wave length of the emitted light of which is 660 nm (red light), and the other is a light emitting diode LED 2, the wave length of the emitted light of which is 940 nm (infrared light). On the other hand, a photo-diode is used for the light receiving section 14.
The above two light emitting diodes LED 1 and LED 2 alternately emit light when they are alternately energized by the timing generation circuit 22, which is provided in the measurement apparatus body 20 via the light emitting diode driving circuit 23 at a predetermined timed relation.
As described above, rays of light are outputted from the respective light emitting diodes LED 1 and LED 2 in the light emitting section 12 and transmitted through a living tissue such as a finger 16. Then the rays of light arrive at the light receiving section 14. Intensities of these rays of light, the wave lengths of which are 660 nm and 940 nm, are converted into currents by the photo-diodes. The thus obtained currents are converted into voltages by the current/voltage converter 24 arranged in the measurement apparatus body 20. At the same time, these signals are separated into transmitted light signals of the respective wave lengths by the demodulator 25.
Then, the pulse wave components (xcex94A660, xcex94A940) of each absorbance are taken out from the two transmitted light signals, which have been obtained by the demodulator 25, by the pulse wave component detectors 26a, 26b of each wave length. Ratio "PHgr" of absorbance (=xcex94A660/xcex94A940) is calculated by the absorbance ratio calculator 27. Further, the oxygen saturation S [=f("PHgr")] is converted by the oxygen saturation converter 28.
However, the pulse oximeter has come into wide use as a vital sign signal monitor, because it is possible for the pulse oximeter to make a continuous non-invasive measurement and further it is unnecessary to make a calibration by principle when the pulse oximeter is used, that is, the pulse oximeter meets the essential requirements necessary for the monitor to be used for monitoring a condition of a patient. Accordingly, various pulse oximeters, in which the apparatus arrangement shown in FIG. 14 is used, are manufactured and sold by a large number of manufacturers nowadays.
For example, as a lead connection system for connecting the probe 10 with the measurement apparatus body 20 in the conventional pulse oximeter in which two light emitting diodes are used, there are provided two lead connection systems. One is a three line system shown in FIG. 17, and the other is a two line system shown in FIG. 18.
As shown in FIG. 17, in the three line connection system, two light emitting diodes LED 1 and LED 2 are connected in parallel to each other by the common line LED-COMMON and two driving lines LED-DRV1, LED-DRV2. As shown in FIG. 18, in the two line connection system, two light emitting diodes LED 1 and LED 2 are connected in reverse-parallel to each other by two driving lines LED-DRV1, LED-DRV2.
As a variation of the lead connection system, there is provided a lead connection system in which four light emitting diodes LED 1 to LED 4 are connected by the three line system as shown in FIG. 19. Also, there is provided a lead connection system in which three light emitting diodes LED 1 to LED 3 are connected by the three line system as shown in FIG. 20. In the lead connection system shown in FIG. 20, one of the light emitting diodes incorporated into the lead connection system shown in FIG. 19 is omitted.
In this case, for example, in the pulse oximeter in which the three line type lead connection system is used, it is preferable that the three line type probe and the two line type probe can be connected with one measurement apparatus body being compatible with each other and the light emitting diode of each probe can be appropriately driven. However, although the light emitting diode in the three line type probe and the light emitting diode in the two line type probe respectively have two driving lines LED-DRV1 and LED-DRV2, their electrical connection system are different from each other. Therefore, the three line type probe and the two line type probe are not compatible with each other, that is, it is impossible to appropriately drive the light emitting diode of each lead connection system with compatibility.
It is an object of the present invention to provide a current driving system of a light emitting diode provided in that: only when a simple additional circuit is arranged in a light emitting diode driving circuit, various probes can be used being made compatible with each other when they are connected with the measurement apparatus body without changing the basic structure of the circuit of the measurement apparatus body and without providing a redundant connection means and without being restricted by the lead connection system of the light emitting diode on the probe side.
In order to accomplish the above objects, the present invention provides a current driving system of a light emitting diode including an apparatus for measuring the concentration of light absorbing material in a living tissue, the apparatus for measuring the concentration of light absorbing material having a probe attached to the living tissue and also having a measurement apparatus body combined with the probe for calculating the concentration of light absorbing material in the living tissue, the probe having a light emitting section composed of at least two light emitting diodes of different wave lengths of emitted light and also having a light receiving section composed of a photo-diode for receiving light emitted from the light emitting section and transmitted through the living tissue, the light emitting diodes being successively and continuously driven by a light emitting diode driving circuit arranged in the measurement apparatus body, the current driving system of a light emitting diode provided in that:
three current supply lines and connection terminals thereof for respectively driving the light emitting diodes on the probe side are arranged in a light emitting diode driving circuit on the measurement apparatus body side;
a pair of driving switches having contact points to be switched to the electric power source side or the ground side are respectively connected with the two current supply lines among the three current supply lines; and
switching operation signal supply lines are arranged for successively and continuously driving the light emitting diodes by supplying a switching operation signal for switching the contact points on the electric power source side or on the ground side to the pair of driving switches.
In this case, the three current supply lines for respectively driving the light emitting diodes are respectively connected with the first driving line and the second driving line of the probe and also connected with the common line so that at least two light emitting diodes can be successively and continuously driven on the probe side.
The switching operation signal supply line is connected and arranged so that the light emitting diodes can be successively and continuously driven when a contact point switching operation is simultaneously conducted on the contact point of one pair of driving switches by which switching is made onto the electric power source side and also conducted on the contact point of the other pair of driving switches by which switching is made onto the ground side with respect to each pair of driving switches and also when a contact point switching operation is simultaneously conducted on the contact point of one pair of driving switches by which switching is made onto the ground side and also conducted on the contact point of the other pair of driving switches by which switching is made onto the electric power source side with respect to each pair of driving switches.
The three current supply lines for respectively driving the light emitting diodes are respectively connected with the first driving line and the second driving line of the probe and the other current supply line is in an unconnected state with the probe. In this case, the terminal of the unconnected current supply line is arranged as a dummy terminal, which is not used.
The switching operation signal supply line is connected and arranged so that the contact points switched and connected with the electric power side and the ground side of the respective driving switches can be independently switched by the pair of driving switches respectively connected with the two current supply lines, the third driving switch having a contact point for switching between the electric power source side and the ground side is arranged in the other current supply line, and a switching operation signal supply line is connected and arranged which is used for switching the contact point of the third driving switch corresponding to the switching signal supplied to the switching signal supply line of the pair of driving switch.
The three current supply lines for respectively driving the light emitting diodes are composed in such a manner that three or four light emitting diodes, in which on the probe side two light emitting diodes are connected in reverse-parallel to each other and one or two light emitting diodes are connected with each other in parallel to them in reverse-parallel to each other, are respectively connected with the first driving line and the second driving line, which are successively and continuously driven, and also connected with the common line.
The probe is composed in such a manner that reverse-parallel diodes are connected between the common line and one driving line, and the reverse-parallel diodes are connected with the common line and the other driving line, so that the four light emitting diodes are respectively, successively and continuously driven.
The probe is composed in such a manner that reverse-parallel diodes are connected between the common line and one driving line, and the diodes are connected with the common line and the other driving line, so that the three light emitting diodes are respectively, successively and continuously driven.
The switching operation signal supply line is connected and arranged so that the contact points switched and connected with the electric power side and the ground side of the respective driving switches can be independently switched by the pair of driving switches respectively connected with the two current supply lines, the third driving switch having a contact point for switching between the electric power source side and the ground side is arranged in the other current supply line, and a switching operation signal supply line is connected and arranged which is used for switching the contact point of the third driving switch corresponding to the switching signal supplied to the switching signal supply line of the pair of driving switch.
Four switching operation signal supply lines are respectively connected and arranged as a switching operation signal supply line for switching the contact points of the pair of driving switches respectively connected with the two current supply lines and also as a switching operation signal supply line for switching the contact points of the third driving switch.
The present invention provides a current driving system of a light emitting diode including an apparatus for measuring the concentration of light absorbing material in a living tissue, the apparatus for measuring the concentration of light absorbing material having a probe attached to the living tissue and also having a measurement apparatus body combined with the probe for calculating the concentration of light absorbing material in the living tissue, the probe having a light emitting section composed of at least two light emitting diodes of different wave lengths of emitted light and also having a light receiving section composed of a photo-diode for receiving light emitted from the light emitting section and transmitted through the living tissue, the light emitting diodes being successively and continuously driven by a light emitting diode driving circuit arranged in the measurement apparatus body, the current driving system of a light emitting diode provided in that:
a predetermined number of current supply lines and connection terminals thereof for respectively driving the light emitting diodes on the probe side are arranged in a light emitting diode driving circuit on the measurement apparatus body side;
driving switches having contact points to be switched onto the electric power source side or the ground side are connected with the predetermined number of current supply lines in the current supply lines;
the probe is compatible with a probe, the number of light emitting diodes of which is different, and also compatible with a probe, the connection system of which is different; and
a switching operation signal supply line for switching the driving switch so as to successively and continuously drive the light emitting diodes is arranged.
The driving switch may be composed of an ON-OFF switch and a switch for constant current.